Rotary fuel pumps driven by an electrical powering device have been utilized for some years in some vehicles either as original equipment or as appliances to supplement the original fuel supply system. The pump and power unit are frequently in a common housing as shown, for example, in U.S. Pat. No. 4,401,416, issued Aug. 30, 1982 to Charles H. Tuckey.
Since the pumps are frequently mounted in the fuel tanks of a vehicle, the noise factor is extremely important. A pump under load will normally produce more noise and this may be audible as a humming noise, to an annoying degree, to passengers in the vehicle.
It will be appreciated that in the pumping cycle, as one pumping cell is exhausting, another cell is taking in fluid at the same time. In other words, intake and exhaust pressure waves are timed with one another, and normally the quantity of fluid being exhausted from each cell is the same as that being taken in by another cell.
It is an inherent characteristic of a positive displacement pump to produce slight pressure pulses each time one of the multiple vanes passes through its pumping cycle. For example, a roller vane rotary pump produces an audible humming noise when operating at system pressure. This noise has a tendency to increase as the output pressure requirement is increased.
It has been a desire of manufacturers and users of positive displacement rotary pumps to reduce or eliminate pressure pulses in order to achieve a smooth, pulse-free flow of fluid out of a pump at desired operating pressure.
An object of the present invention is to allow the exhaust pressure peaks to counter the negative inlet pressure valleys thereby cancelling one another and attaining a smooth flow in and out of the assembly and at the same time reducing the pump noise.
This concept involves the utilization of a resilient member between the inlet and exhaust zones within the pump assembly. Thus, each time a pressure peak occurs in the exhaust fluid, the pressure can force the resilient member to yield or move toward the inlet fluid, thereby simultaneously off-setting the negative pressure which occurred at the same time on the inlet side.
It has been noted that pressure waves or pulses are preset at the inlet, as well as the outlet, at all operating pressures.
One must acknowledge and deal with the extreme pressure differential between the inlet and exhaust sides of the pump. For instance, the inlet zone is usually at an average pressure close to atmospheric; and the outlet zone average pressure is much higher, i.e., 60 psi or more depending upon the operating pressure requirement of the pump.
Hollow pulse absorbing chambers in fuel pumps have been proposed previously as exemplified in U.S. Pat. No. 4,181,473 to Yoshifumi issued Jan. 1, 1980 and U.S. Pat. No. 4,521,164 to Tuckey issued June 4, 1985.
In the present invention a hollow pulse modulator of a flexible plastic material is proposed formed by a blow molding process in which the internal pressure within the walls of the hollow chamber is above atmospheric and introduced into the chamber during the molding process.
Other objects of the invention will be apparent in the following description and claims in which the invention is described, together with details to enable a person skilled in the art to practice the invention all in connection with the best mode presently contemplated for the invention.